Emsley also took liberties with Middleton's eye color, changing it slightly to match the blouse she is wearing in the painting.

While the painting reveals a more mature Middleton, art critics are slamming Emsley's work, saying it looks nothing like her.

"Seriously, as a concept, what is it? It's like a giant Polaroid. Like she went into a photo booth and had that picture taken and blown up to a huge size it would look more or less the same, wouldn't it," Waldemar Januszczak, art critic for The Sunday Times, said.

Middleton, 31, sat twice for the portrait - once in May and again in June. She reportedly described the work as "amazing," adding, "I thought it was brilliant."

William said, "It's absolutely beautiful."

It was a rare appearance for the Duchess of Cambridge, who was released from the hospital in December, as she battles severe morning sickness known as hyperemesis gravidarum.